package snowflake;

public class IdWorker {
    private long workerId;
    private long datacenterId;
    private long sequence;

    public IdWorker(long workerId, long datacenterId, long sequence) {
        if (workerId > maxWorkerId || workerId < 0) {

        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
        this.sequence = sequence;
    }


    private long twepoch = 1288834974657L;
    private long workerIdBits = 5L;
    private long datacenterIdBits = 5L;
    //二进制运算，就是5bit最多只能有31个数字，也就是说及其id最多只能是32以内
    private long maxWorkerId = -1L ^ (-1L << workerIdBits);
    private long sequenceBits = 12L;
    private long workerIdShift = sequenceBits;
    private long datacenterIdShift = sequenceBits + workerIdBits;
    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private long sequenceMask = -1L ^ (-1L << sequenceBits);

    private long lastTimestamp = -1L;

    public long getWorkerId() {
        return workerId;
    }

    public long getDatacenterId() {
        return datacenterId;
    }

    public long getTimestamp() {
        return System.currentTimeMillis();
    }


    public synchronized long nextId() {
        long timestamp = timeGen();
        if (lastTimestamp == timestamp){
            //这个意思是说一个毫秒内最多只能有4096个数字
            //无论你传递多少进来，这个位运算保证始终就是在4096这个范围内，避免你自己传递个sequence超过限制大小
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0){
                timestamp = tilNextMillis(lastTimestamp);
            }
        }else{
            sequence = 0;
        }
        //记录一下最近一次生成id的时间戳，单位是毫秒
        lastTimestamp = timestamp;
        //时间戳左移，放到41 bit；
        //将机房 id左移放到5 bit；
        //将机器id左移放到5 bit那儿；将序号放最后12 bit；
        //最后拼接起来成一个 64bit的二进制数字，转换成10进制就是个long型
        return ((timestamp - twepoch)<<timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
    }

    private long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp){
            timestamp = timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }

}
